Hydroponic Troubleshooting Guide

Plants communicate through their leaves. Learning to read these signals transforms troubleshooting from guesswork into diagnosis. This guide covers the problems you'll actually encounter.

## Quick Diagnosis Chart

The honest truth: 90% of problems trace back to pH. Always check pH first. It's the cause more often than you'd expect.

## Yellow Leaves

The most common question. Yellowing means something, but what depends on which leaves and how they yellow.

Older leaves yellowing (bottom of plant first): Usually nitrogen deficiency. Plants move nitrogen from old leaves to new growth when supply is short.

Fix: Check pH first (nitrogen lockout above pH 7). If pH is fine, increase nitrogen or overall nutrient strength.

Younger leaves yellowing with green veins: Iron deficiency (interveinal chlorosis). Almost always caused by high pH - iron becomes unavailable above pH 6.5.

Fix: Lower pH to 5.5-6.0. Iron deficiency corrects within days once pH is right.

All leaves pale yellow-green: General nutrient deficiency. Either solution is too weak or pH is locking out multiple nutrients.

Fix: Check EC/TDS. If adequate, check pH. Fresh solution often resolves this.

Yellow spots or mottling: Various causes - could be potassium deficiency, calcium deficiency, or pest damage. Look for other clues.

## Root Problems

Healthy roots are white or cream-coloured, firm, and smell neutral. Any deviation is worth investigating.

Brown, slimy roots: Root rot. Caused by pathogens that thrive in warm, low-oxygen conditions.

Causes: Water too warm (above 22C), insufficient oxygen (DWC without adequate bubbling), stagnant water, contaminated equipment.

Fix: Remove affected plants. Clean system thoroughly. Start fresh with cooler water. Add more aeration. Consider beneficial bacteria products like Hydroguard.

Brown but firm roots: Nutrient staining. Some fertilisers dye roots brown. This is cosmetic, not harmful.

How to tell: Stained roots stay firm and functional. Rotted roots are slimy and smell bad.

Minimal root growth: Could be too-strong nutrients (roots burn back), too-weak nutrients (nothing to grow toward), or environmental stress.

Fix: Check EC (should be appropriate for growth stage). Check water temperature (18-22C ideal). Ensure light isn't reaching roots.

## Algae

Green growth on surfaces, in solution, or on growing medium. More nuisance than crisis but worth addressing.

Cause: Light reaching nutrient solution. Algae photosynthesises like plants - give it light and nutrients and it grows.

Problems: Competes with plants for nutrients. Can clog drippers and lines. Creates smell. Looks bad.

Prevention: - Use opaque containers - Cover reservoirs completely - Block light from reaching any solution - Black tape over any light leaks

Treatment: Remove affected solution. Clean surfaces. Block light sources. Start fresh.

## pH Problems

pH rising constantly: Plants consuming nutrients faster than they consume water. The solution becomes more concentrated and alkaline as the buffering capacity depletes.

Fix: Change solution more frequently. Consider using larger reservoir for more stable chemistry.

pH dropping constantly: Less common. May indicate bacterial activity in reservoir or decomposing organic matter.

Fix: Clean system thoroughly. Check for dead roots or decaying plant material. Change solution.

pH won't adjust: Hard water with high mineral content resists pH change. Your area's water is heavily buffered.

Fix: Use more pH adjuster (carefully). Consider rainwater or filtered water for some of your mix.

## Wilting

Wilting with dry reservoir: Simple - plants need water. Refill.

Wilting with plenty of water: Root damage. Plants can't transport water despite it being available. Check roots for rot.

Wilting in hot conditions: Heat stress or transpiration exceeding uptake. Increase airflow, reduce temperature if possible, ensure roots have access to water.

Wilting that recovers overnight: Often normal on hot days. Plants wilt during high transpiration and recover when it's cooler. Mild wilting in afternoon heat isn't necessarily a problem if plants look fine by morning.

## Slow Growth

Check light first. Insufficient light is the most common cause of slow growth indoors. Herbs need 12-16 hours of adequate light. Move closer to light source or add more lighting.

Check temperature. Growth slows below 15C and above 30C. Most vegetables prefer 18-25C.

**Check nutrients.** Low EC limits growth potential. If light and temperature are fine, increase nutrients slightly.

Check roots. Root problems restrict nutrient uptake regardless of what's in the solution.

## Pests

Fungus gnats: Small flies whose larvae eat roots. They love wet growing media.

Fix: Let media surface dry between waterings (if using media). Use yellow sticky traps. Sand layer on surface deters egg-laying.

Aphids: Appear seemingly from nowhere. Check new plants carefully before adding to your system.

Fix: Blast off with water spray. Use insecticidal soap. Introduce ladybirds if growing in a greenhouse.

Spider mites: Tiny, cause stippled leaves. Thrive in hot, dry conditions.

Fix: Increase humidity. Spray with water. Use neem oil or insecticidal soap.

## What to Avoid

Changing multiple things at once: Change one variable, wait 3-5 days, observe. Changing everything simultaneously means you won't know what worked.

Panicking: Plants are resilient. Most problems are fixable if caught early. A few yellow leaves aren't a crisis.

Overwatering media-based systems: Just because it's hydroponics doesn't mean roots should be constantly wet in flood-and-drain or drip systems.

**Adding more nutrients to fix problems:** Usually makes things worse. Diluting is often better than adding.

## The Diagnostic Process

1. Check pH (it's almost always pH) 2. Check EC/TDS 3. Check water temperature 4. Check roots directly 5. Check light levels 6. Check for pests

This order catches 95% of problems. Work through systematically rather than guessing.

Take our quiz if you want recommendations for your specific setup.